next hop determination in ospf...

[jemekeren]

Hi.. in rip or distance vector protocols. the next hop is determined from neighbor source ip, right? but in ospf(linkstate protocol) how next hop is determined? it makes me more confused in broadcast network where DR is used. how router know where is the next hop if information is spread from DR. is it from lsa field? i see lsa has no info about nexthop... please explain me... TX ;)

[royalblues]

Friend,

If you see the LSA details you will find something like a advertising router field.

SO when a DR sends a packet it would set the advertising router field to be the IP of the router advertising that LSA. This way it would come to know the nexthop router

Eg..see the 20.20.20.0 network is not advertised by DR but another router in the broadcast network

LS age: 369

Options: (No TOS-capability, DC)

LS Type: Router Links

Link State ID: 10.10.10.1

Advertising Router: 10.10.10.1

LS Seq Number: 80000005

Checksum: 0x5014

Length: 48

Number of Links: 2

Link connected to: a Stub Network

(Link ID) Network/subnet number: 20.20.20.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 1

Link connected to: a Transit Network

(Link ID) Designated Router address: 10.10.10.2

(Link Data) Router Interface address: 10.10.10.1

Number of TOS metrics: 0

HTH, rate if it does

Narayan